Device with a prosthesis implantable in the body of a patient

ABSTRACT

The device comprises a prosthesis designed as a hollow body compressed against the action of restoring spring forces to a cross section reduced relative to an expanded use position, and held in this position by a strippable sheath. After the sheath is stripped, the prosthesis automatically expands to a cross section corresponding to the use position. The sheath, which can be a meshwork in the approximate form of crocheted material, extends over the entire length of the prosthesis and consists of at least one continuous thread and at least one drawstring. The prosthesis, held in the radially compressed position by the sheath, can be mounted displaceably on a feed wire or non-axially-displaceably on the insertion end of a probe or a catheter.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/567,735 filed on Dec.5, 1995 now U.S. Pat. No. 5,653,748, which is a file-wrappercontinuation of application Ser. No. 08/420,135, filed Apr. 11, 1995,now abandoned, which is a continuation of application Ser. No.07/886,518, filed May 20, 1992, now U.S. Pat. No. 5,405,378.

BACKGROUND OF THE INVENTION

The invention relates to a device with a prosthesis implantable in thebody of a patient, especially in a blood vessel or other body cavity,and designed as a hollow body, said prosthesis being compressibleagainst the action of restoring spring forces down to a cross sectionwhich is reduced relative to an (expanded) operating position, saidprosthesis also automatically expanding to a cross section correspondingto the operating position following removal of the restraining forceseffecting the compression.

Devices of this type are known, and serve for percutaneous implantationof vascular prostheses in particular. Prostheses which are introduciblepercutaneously and expand in the lumen are either expandablemechanically by means of a known balloon catheter from a small radius tothe larger radius to hold a vascular lumen open, or they expandautomatically following previous compression prior to implantation byspring force, due to spring pretensioning generated during compression.

Various systems are already known for inserting self-expanding vascularprostheses which are under spring force into the body of a patient, andto implant or anchor them in the vessel by removing the restrainingforce.

The commonest method, which is described in EP-A-0 183 372, consists incompressing an endoprosthesis, made in the form of a tubular hollowbody, to a reduced cross section and then pushing it in the compressedstate, using a so-called pusher, through a catheter previouslyintroduced into a vessel until they are in the correct position in thevessel. However, this system suffers from the disadvantage that aconsiderable expenditure of force is required to push the prosthesisthrough the catheter because its displacement is counteracted byconsiderable frictional forces.

Another method (not confirmable by publications) consists in retractinga sheath covering the endoprosthesis and holding the latter together, inthe vessel at the implantation site. Here again there is thedisadvantage that high frictional forces must be overcome. Moreover, thetube system is quite rigid because of the sheath covering theprosthesis, making introduction into a vessel through curves verydifficult.

In another system (U.S. Pat. No. 4,732,152) a woven and spring-tensionedprosthesis is held together in the compressed state by a double sheath,sealed at the distal end. This sheath is retracted from the foldedprosthesis like a stocking being pulled off the foot of a wearer. Toreduce the friction which then occurs, liquid can be introduced betweenthe two sheath layers. This system, which initially appears elegantbecause of the reduction of the frictional resistances, is extremelycumbersome to handle however and requires two persons to operate.

SUMMARY OF THE INVENTION

The invention is intended to provide an especially simple and readilyoperable device for implantation of a prosthesis made in the form of ahollow body, with a vascular prosthesis envisioned in particular.

This goal is achieved by virtue of the fact that in the device theprosthesis is surrounded by a sheath which can be pulled off it, saidsheath consisting of at least one through thread, and compressed to areduced cross section, and by the fact that at least one drawstring isprovided, said drawstring being laid so it extends away from the sheathholding the prosthesis in its radially compressed state, the threadforming said sheath being retractable.

In the invention, the prosthesis is therefore held in its radiallycompressed state by means of this external sheath and reaches itsintended expansion position only after removal of this sheath, which isdesigned to be pulled off, thanks to the pretensioning force generatedduring compression.

The sheath can be in particular a meshwork produced by crocheting,knotting, tying, or other methods of mesh formation.

Advantageously the prosthesis, held by the sheath which can be pulledoff in the radially compressed state, can be received on a probe, or aflexible guide wire, and advanced thereon. In one design of a device ofthis kind, implantation is accomplished by introducing the guide wire inknown fashion into a vessel and then advancing the prosthesis, held in aradially compressed state, along the guide wire, said wire beingadvanced for example by means of a sleeve likewise advanced over theguide wire and engaging the end of the prosthesis away from theinsertion end thereof.

Another improvement, on the other hand, provides that the prosthesis,held in the radially compressed state by the sheath which can be pulledoff, is held in an axially fixed position on the insertion end of aprobe. Specifically, this probe can be a catheter advanced over a guidewire.

Even with the axially fixed mounting of the prosthesis, held in thecompressed state, on the insertion end of a probe or a catheter,implantation takes place in simple fashion with the probe or catheterbeing advanced together with the prosthesis mounted on the insertionend, for example under the control of x-rays, up to the implantationsite, and then by pulling off the sheath, made for example as a coveringmeshwork, the prosthesis is exposed and implanted in the proper locationby its automatic expansion.

In mounting the prostheses on the insertion ends of probes or catheters,it has been found to be advantageous for the prosthesis to be mounted ona non-slip substrate surrounding the probe or catheter, so thatundesired slipping and sliding during the release of the thread materialforming the meshwork cannot occur.

Advantageously, the self-expanding prosthesis can be a tube made bycrocheting, knitting, or other methods of mesh formation, composed ofmetal and plastic thread material with good tissue compatibility, saidtube being compressible radially against the action of pretensioningforces and automatically expanding into its operating position after therestraining forces are removed, and then remaining in the expandedposition.

In the case of the prosthesis designed as meshwork, according to alogical improvement, successive rows of mesh can be made alternately ofresorbable thread material and non-resorbable thread material. Thismeans that within a predetermined period of time after implantation, theresorbable thread material will be dissolved and the prosthesis parts,then consisting only of non-resorbable thread material, will remain inthe patient's body. These remaining components form circumferentialrings of successive open loops. This avoids thread intersections whichcould exert undesirable shearing forces on surrounding and growingtissue coatings.

In the improvement just described, drugs can also be embedded in theresorbable thread material so that the prosthesis constitutes a drugdeposit which gradually dispenses drugs during the gradual dissolutionof the resorbable thread material.

An especially advantageous improvement on the invention is characterizedby making the tubular meshwork holding the prosthesis in the compressedstate in such a way that the mesh changes direction after each wraparound the prosthesis and when successive meshes are pulled off, thethread sections forming the latter separate alternately to the right andleft from the prosthesis.

The advantage of this improvement consists in the fact that the meshwrapped successively and alternately left and right around theprosthesis can be pulled off without the thread material becomingwrapped around the probe holding the prosthesis or a catheter serving assuch, or undergoing twisting, which would make further retraction of thethread material more difficult because of the resultant friction.

It has also been found to be advantageous in the improvement describedabove for the loops or knots of the mesh wrapped successively around theprosthesis and capable of being pulled off, to be located sequentiallywith respect to one another or in a row running essentially axially.

Another important improvement on the invention provides for thedrawstring to extend away from the mesh surrounding the insertion end ofthe prosthesis, and therefore the prosthesis, as the meshwork is pulledoff its distal end, gradually reaches its expanded position.

In this improvement, the thread material to be pulled off when theprosthesis is tightened can never enter the area between the alreadyexpanded part of the prosthesis and the wall of a vessel for example.The thread material to be pulled off instead extends only along the partof the mesh which has not yet been pulled off and thus in the area ofthe prosthesis which is still held in the compressed position.

The ends of the thread material forming the meshwork can be held byreleasable knots, in the form of so-called slip knots for example, andthereby have their releasability preserved. One especially simple meansthat has been found for axial mounting of the prosthesis on a probe oron a catheter serving as such is for the beginning of the threadmaterial forming the meshwork and an end mesh to be pinched in holes inthe probe or catheter, yet capable of being pulled out of their pinchedpositions by means of the drawstring. The beginning of the threadmaterial can be pinched between the probe and the cuff mounted held onthe latter, however.

The cuff material is held especially securely, but at the same time insuch a way that it can be easily pulled off, if from the knot of themesh of the first mesh on the pull-off side of the meshwork, a looppassed through a hole extends, one end of said loop making a transitionin the vicinity of the above knot to the drawstring. As a result, thisloop can be pulled off by means of the drawstring through theabove-mentioned knot and then all of the mesh forming the meshwork canbe pulled off in succession.

According to another logical improvement on the invention, theprosthesis can also be held in its radially compressed position by meansof a meshwork applied from the distal end of the probe or catheter andextending over the insertion end of the prosthesis and by means of ameshwork that extends in the direction opposite the proximal end andalso extends over the end mesh of the first meshwork. It has been foundadvantageous in this connection for the two meshworks to be capable ofbeing pulled off in opposite directions from their loop-shaped endmeshes by means of drawstrings.

In a design of this kind, following correct placement of the prosthesismounted on a probe or a catheter in a vessel, the meshwork applied fromthe distal end is pulled off first, beginning with the end mesh removedfrom the distal end and then advancing gradually until this meshwork isremoved completely and the thread material is retracted. Then themeshwork applied from the proximal end is pulled off, starting with theend mesh toward the distal end and then advancing toward the proximalend. It is obvious that when the meshwork is pulled off in this way, theself-expanding prosthesis is expanded gradually, starting at its distalend, into its intended operating position.

In another important embodiment, the sheath that holds the prosthesis inits radially compressed position consists of loops surrounding theprosthesis and spaced axially apart, said loops being formed by thethread material, pulled through a hole in the prosthesis, of a threadguided along inside the prosthesis,.with the ends of the loops eachbeing brought back through a hole, adjacent to the first hole in thecircumferential direction, into the interior of the prosthesis, and awarp thread, likewise running along the inside of the prosthesis andguided through the ends of the loops, holds in the loops in theirwrapping positions. It is clear that in this design the prosthesis isreleased by pulling the warp thread out of the end segments of theloops, and that the thread material forming the loops,like the warpthread, can be retracted in simple fashion. In a similar improvement onthe invention, the sheath holding the prosthesis in its radiallycompressed position consists of loops which are axially spaced apart andare wrapped around the prosthesis, said loops being formed by threadmaterial, pulled through a hole in the prosthesis, of a thread guidedalong inside the prosthesis, with the ends of the loops each beingbrought back into the interior of the prosthesis through holes spacedaxially from the first hole, and held in place by the fact that a loopformed from the thread material running inside the prosthesis is pulledthrough each loop end brought back into the prosthesis, said loop thenbeing brought out through a hole following in the axial direction, thenbeing wrapped around the prosthesis and brought back in the same mannerwith its loop end passing through a hole into the prosthesis and beingsecured in this position. In this design also, the pulling off of thesheath holding the prosthesis in its radially compressed position isaccomplished in simple fashion by means of the thread extending from thelast loop, from which the loops surrounding the prosthesis are formed.

For especially tight wrapping and the resultant compression of theprosthesis, it has also been found advantageous to use shrinkable threadmaterial to form the meshwork. The meshwork that can be pulled off canalso consist of a plurality of threads running parallel to one another.

Another important improvement on the invention provides that between theprosthesis and the sheath holding the latter in the radially compressedstate, at least one additional sheath is provided which loosely fitsaround the prosthesis and allows a partial expansion of the prosthesiswhen the outer sheath is pulled off, and is itself subsequently capableof being pulled off.

This improvement is also one that involves a sheath, surrounding theprosthesis loosely and with a certain amount of play, being mounted onsaid prosthesis, which can be a meshwork, with the prosthesis and theinner sheath being surrounded closely by an outer sheath which holds theprosthesis, together with the sheath mounted directly on it, in theradially compressed state. The prosthesis is consequently surrounded bytwo layers, so to speak, and after the outer sheath is stripped, canexpand only within the limits set by the inner sheath. The finalimplantation is then accomplished by stripping the inner sheath, i.e. instages.

Of course, several meshworks surrounding one another with a certainamount of play can be provided, which permit expansion of the prosthesisin several successive stages.

Within the scope of the invention, the spaces between the meshes of ameshwork surrounding the prosthesis and holding it in the compressedstate can be filled and smoothed with gelatin or a similar substancewhich dissolves in the body of a patient. This facilitates introductionof such a device.

According to yet another improvement, at least one end of the prosthesiscan be surrounded in the compressed state by a cuff, said end, becauseof the axial shortening of the prosthesis that takes place duringexpansion, escaping the grip exerted by the cuff. A cuff of this kindcan be mounted permanently on the probe and/or a catheter, with the openside facing the prosthesis, for example on the side toward the distalend. This produces a smooth transition that facilitates introduction, atthe end of the prosthesis which is at the front in the insertion device.

For improved attachment of the prosthesis to a probe or a to catheterserving as same, the end of the prosthesis facing away from theinsertion end can abut the end of the prosthesis away from the insertionend at a radially projecting step or shoulder or a cuff mounted on theprobe or catheter.

Yet another improvement on the invention provides that when a catheteris used as a probe, the drawstring is introduced through a hole passingthrough the catheter wall in the vicinity of one end of the prosthesis,enters the lumen of the catheter, extends through the latter, andextends beyond the end of the catheter.

However, a double-lumen catheter can also serve as a probe with onelumen serving to advance the catheter over a guide wire and the otherlumen being used to guide the drawstring.

When using a catheter with one or two lumina as a probe, with thedrawstring passing through the catheter lumen, assurance is providedthat the walls of the vessels or other body cavities in which aprosthesis is to be implanted cannot be damaged by the drawstringand/or, when the meshwork is stripped, by the thread material, which isthen pulled back through the catheter lumen.

It has also proven to be advantageous for the drawstring and/or thethread material of the meshwork to be provided with a friction-reducinglubricant.

In addition, at least the drawstring can be made in the form of a metalthread or provided with an admixture of metal, so that good visibilitywith x-rays is ensured.

Finally, according to yet another improvement, the prosthesis, kept inthe radially compressed position by the strippable sheath, can expand toresemble a trumpet at its proximal end in the expanded state followingremoval of the sheath. This prosthesis design is important for implantsin the vicinity of branches in the vessels, because there is always thedanger of the prosthesis slipping into the branching vessel. In view ofthe trumpet-shaped expansion at the proximal end, however, such slippingduring implantation is effectively suppressed when the sheathsurrounding the prosthesis is stripped off the proximal end.

One embodiment of the device according to the invention will now bedescribed with reference to the attached drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a catheter with a vascular prosthesis mounted on its distalend held under radial pretensioning in the compressed state by acrocheted material in the form of a strippable tubular meshwork;

FIG. 2 is a view showing the formation of an initial mesh of crochetedmaterial on the prosthesis, with a loop brought around the vascularprosthesis on the right side;

FIG. 3 is a view like that in FIG. 2, showing the formation of acrocheted mesh adjoining the initial mesh, wrapped around the vascularprosthesis on the left side;

FIG. 4 is a view similar to FIG. 1 showing a design for a device inwhich the vascular prosthesis mounted on the catheter is held in itscompressed state with radial pretensioning by means of strippablecrocheted material mounted on the distal and proximate ends;

FIG. 5 shows the device according to FIG. 4 but with the crochetedmaterial applied from the distal end;

FIG. 6 shows the device according to FIG. 4 with the crocheted materialapplied from the proximal end alone, eliminating the crocheted materialshown in FIG. 5;

FIG. 7 shows the vascular prosthesis alone, held in a radiallycompressed position by wrapping loops;

FIG. 8 is a view like that in FIG. 7 of a prosthesis in which the loopsholding the latter in a radially compressed position are formed bycrocheting, and

FIG. 9 shows partial stripping of a vascular prosthesis in the form ofknitted fabric.

DETAILED DESCRIPTION OF THE INVENTION

In device 10 shown in FIG. 1, an elongated catheter 11 serves as aprobe, with a through lumen by which the catheter can be advanced inknown fashion over a guide wire inserted in a vessel. In the vicinity ofits distal end 12, catheter 11 carries a prosthesis 15 held in acompressed position under radial pretensioning by means of a crochetedmaterial 14, said prosthesis, following elimination of the restrainingforce provided by the crocheted material, changing to its intendedexpanded position by expanding automatically. For example, theprosthesis can be a tubular knitted fabric radially compressible againstthe effect of a restoring spring force into a position in which it fitsclosely around the catheter in the vicinity of its distal end.

Prosthesis 15 is surrounded by a crocheted material 14 formed by acontinuous thread, with successive meshes wrapped around the prosthesisalternately on one side or the other, in other words alternately on theright or left side. The initial section 17 of the thread material,located in front of the first mesh 16 associated with the distal end 12of catheter 11, is pulled through a slot 18 in the catheter wall,pinched in said slot, and then extends through the catheter lumen andout through the distal end of the catheter. A strippable loop 22 ispulled through a knot 21 that closes end mesh 21 which is remote fromthe distal end, said loop being pulled through two rejected [sic."beanstandete"] cuts 23, 23' in the catheter wall, and is thereforelikewise held axially by pinching.

The free thread end guided through knots 21 of said end mesh 20 forms adrawstring 24 extending along catheter 11, by means of which drawstring,first loop 22 held on the catheter by pinching and then gradually themesh formed of crocheted material extending around the prosthesis andholding the latter in its compressed state, can be stripped through saidend knot. Since the meshes are wrapped alternately right and left aroundprosthesis 15, when the mesh is stripped the threads on the right andleft sides of the catheter are released alternately from thecorresponding mesh knots, and after the mesh facing the distal end comesloose, initial segment 17 of the thread material can be pulled out ofits pinched position in slot 18 at distal end 12 of catheter 11.

In an enlarged view, FIGS. 2 and 3 show the mesh formation withalternate front and back wrapping of catheter 15, which in these figuresis shown as a rigid tubular structure for the sake of simplicity. Aftersecuring initial section 17 of the thread material in the manner shownin FIG. 1 by pinching in slot 18, the thread is wrapped around thecatheter, then a loop 26 is pulled through under the thread, and thenfrom free thread material 27, a mesh on the back of the catheter ispulled around the latter and passed through loop 26, whose sectionpulled through the above loop 26 in turn forms a loop 28 to form thenext mesh. FIG. 2 shows free thread material 27 in solid lines before itis pulled through loop 26, and shows it in dashed lines after it ispulled through this loop and forms loop 28 for the next mesh.

To form the next mesh, as shown in FIG. 3, forming another loop 30 inthe manner shown by the dashed lines, the free thread material is pulledout of the position shown at 31 in front of the catheter, throughpreviously formed loop 28, and then this process of loop and meshformation is continued, with the thread material pulled alternatelybehind and in front of the catheter through the respective loops untilthe prosthesis held in the catheter is crocheted over its entire length.

Loop 22, pulled through the loop associated therewith or through a knot21 formed by pulling together these loops to form end mesh 20, is thenpulled in the manner shown schematically in FIG. 1 through the twoaxially spaced slots 23, 23' in the wall of the catheter and held inplace by pinching. The remaining thread material then forms drawstring24 which extends from the loop of end mesh 20 and permits the crochetedmaterial to be stripped, with the thread material of the meshes as theyare stripped alternately coming loose on one side or the other ofprosthesis 15, thereby releasing the prosthesis to expand under thepretensioning force imposed during crocheting as a result of radialcompression.

In embodiment 40 shown in FIG. 4, a prosthesis 45 is mounted and held inits compressed position under radial pretensioning on an elongatedcatheter 41 in the vicinity of distal catheter end 42. This purpose isserved by crocheted material 46, 47 shown in FIGS. 5 and 6. Catheter 41,like catheter 11 of the embodiment shown in FIG. 1, is advanceable bymeans of a guide wire located in a vessel, in said vessel so thatprosthesis 45 mounted on the catheter is implantable positionwise in thevessel prior to its implantation by stripping the crocheted material.

The crocheted material that holds prosthesis 45 in the compressedposition shown in FIG. 4 is applied sequentially, with crochetedmaterial 46 starting at the distal end. The other crocheted material 47is applied from the proximal end and then overlaps the end of the firstcrocheted material 46.

FIG. 5 shows that catheter 41 is provided on the distal end with asilicone cuff 43, which serves to hold the initial segment 48 of thethread required for the formation of the first crocheted material. Forthis reason, initial segment 48 of this thread is pulled through beneathsilicone cuff 43. Then the first meshes 49, in the manner explainedabove in conjunction with FIGS. 1 to 3, are crocheted on catheter 41,and provide a firm seat on the catheter for the first crochetedmaterial. subsequent meshes 50 fit over the end of prosthesis 41 thatpoints toward the distal end of the catheter, and compress the latterunder radial pretensioning with simultaneous axial immobilization of theprosthesis on the catheter, as shown in FIG. 5. A final mesh 51 of thiscrocheted material 46 is then applied externally on prosthesis 45, withthread 52 extending from this mesh as a drawstring to strip the mesh ofthe above-mentioned crocheted material.

FIG. 6 shows the application of the second crocheted material 47 fromthe proximal end. Beginning 55 of the thread material of this crochetedmaterial is again held by means of a silicone cuff 54 pulled onto theproximal end of catheter 41, while the beginning of the thread is pulledthrough beneath this cuff. Then several meshes 56 are crocheted onto thecatheter in the direction of the distal end, followed by additionalmeshes 57, while wrapping prosthesis 41 during its simultaneous radialcompression up to and beyond meshes 50, 51 of the first crochetedmaterial 46 facing away from the distal end, which are held thereby. Alast mesh 58 of the crocheted material 47 applied from the proximal endis then pulled through under silicone cuff 43 pushed onto the distal endof the catheter, and held thereby. In addition, thread 60 extends fromthe end mesh facing the distal end of the crocheted material 47 appliedfrom the proximal end, as a drawstring to strip the mesh of thiscrocheted material.

The prosthesis 45 in the embodiment shown in FIGS. 4 to 6, like that inthe embodiment shown in FIGS. 1 to 3, is held under radial pretensioningin the compressed position on catheter 41 and automatically expands toits expanded position after removal of crocheted material 46, 47.Following introduction of the prosthesis mounted on the catheter into avessel and its location in place, implantation occurs in such fashionthat crocheted material 46 applied from the distal end is removed first.This is accomplished by stripping the mesh of this crocheted material bymeans of drawstring 52, with mesh 51 located beneath the crochetedmaterial applied from the proximal side being stripped first and thengradually meshes 50 and 49 abutting the distal end being stripped untileventually the first mesh adjacent to silicone cuff 43 comes free andthe beginning of thread 48 beneath the silicone cuff is pulled out.

Since the end of the prosthesis that points toward the distal catheterend is released by stripping crocheted material 46 applied from thedistal end, this end of the prosthesis expands radially as a result ofthe pretensioning forces of the prosthesis itself, while the remainingpart of the prosthesis is still held in the compressed position bycrocheted material 47 applied from the proximal end. Partially expandedprosthesis 45 is axially immobilized in this position both by theadhesive effect between the catheter and the prosthesis and by asilicone cuff 62 mounted on the proximal end of prosthesis 45 oncatheter 41, which cuff the prosthesis abuts axially.

After stripping first crocheted material 46, crocheted material 47applied from the proximal end is also stripped, specifically by means ofdrawstring 60 extending from its end mesh 58 on the side pointing towardthe distal end. It is clear that when the drawstring is pulled, loop 58held at the distal end beneath silicone cuff 43 is stripped first andthen meshes 57 and 56 are stripped, starting at the side facing thedistal end, gradually in the direction of the proximal end, withprosthesis 45 expanding radially and abutting the walls of a vessel tobe equipped with a prosthesis. At the end of the stripping process,thread end 55 located beneath silicone cuff 54 at the proximal end ispulled free. Prosthesis 45 is then free of catheter 41 and the lattercan be withdrawn in simple fashion out of the vessel.

Prosthesis 70 shown in FIG. 7 is likewise tubular in shape andself-expanding. It can be a meshwork, roughly in the form of a knittedfabric. The prosthesis is provided with holes 71, 72 associated with oneanother pairwise and located at approximately equal axial distances fromone another. Loops 74 surrounding the prosthesis externally hold theprosthesis together in its radially compressed state. These loops arethread material, each pulled through a hole 71, of a thread 75 runningalong the inside of the prosthesis, said thread then surrounding theprosthesis forming a loop with tension, and with loop end 76, each beingintroduced through a hole 72 corresponding to matching hole 71, backinto the interior of the prosthesis. The loops are held in the wrappingposition shown in FIG. 7 by means of a warp thread 78 guided throughloop ends 76 inside the prosthesis.

The advantage of the embodiment shown in FIG. 7 consists in the factthat loops 74 wrapped around the prosthesis at essentially constantaxial intervals are used as means for radial compression. of prosthesis70, said loops having no external knots at all but formed by a thread 75running along the inside of the prosthesis and held in the tensionedposition by means of the warp thread 78 likewise running along theinside of the prosthesis.

The prosthesis according to FIG. 7, in the same way as described abovein conjunction with FIGS. 1 to 6, is mounted in a radially compressedstate on a catheter in the vicinity of the distal catheter end, and isimplantable by means of the catheter by advancing the latter in avessel. Following correct positioning in the vessel, implantation isaccomplished in simple fashion by pulling warp thread 78 out of ends 76of loops 74, whereupon prosthesis 70 expands radially under its ownspring pretensioning force to its proper expanded position. Thread 75which is pulled to form the loop can then likewise be simply pulledback.

The embodiment shown in FIG. 8 differs from the embodiment in FIG. 7 inthat loops 74 surrounding prosthesis 70' and spaced axially apart areformed by crocheting. Through a hole 71' in the prosthesis, threadmaterial from thread 75 guided along the interior of the prosthesis ispulled out and wrapped as a loop 74' around the prosthesis, and is alsointroduced through a hole 72' spaced axially from above-mentioned hole71', together with loop end 76', back into the interior of theprosthesis. Thread material is then pulled through this loop end 76'located in the interior of the prosthesis, forming another loop andguided externally through a hole 71' following in the axial direction,then is wrapped again around the prosthesis as loop 74' and secures theloop end, brought back into the interior of the prosthesis throughanother hole 72', in the same manner as the first loop.

Referring to FIG. 9, a knitted intravascular prosthesis 80 (partial viewto illustrate component threads) is shown in which a thread 81 ofresorbable material and a thread 82 of non-resorbable material areknitted together alternately. The non-resorbable thread material can betantalum for example.

The advantage of this prosthesis design consists in the fact that theresorbable thread material dissolves following expiration of apredetermined period of time after implantation, and then only thenon-degradable components remain in the body of a patient. Theseremaining components form circular rings of successive open loops. Inthis manner, thread crossings are avoided, which could exert unnecessaryshearing forces on the surrounding and growing tissue coatings.

Prostheses can also be designed in simple fashion as drug deposits withdrugs being imbedded in the resorbable thread material and released asthis material degrades.

I claim:
 1. A system for use in medical treatment of a body,comprising:a medical apparatus self-expandable from a reduced profilefor inserting the medical apparatus in the body to a expanded profilefor deploying the medical apparatus in the body; a strippable sheathcovering the medical apparatus, the sheath maintaining the medicalapparatus in the reduced profile position; and at least one drawstringextending from the sheath, the drawstring being retractable to permitexpansion of the medical apparatus.
 2. The system of claim 1, whereinthe sheath includes at least one of a crocheted strand and knottedstrand.
 3. The system of claim 2, wherein at least one of the crochetedstrand and knotted strand includes a releasable knot retaining a portionof the strand at an end of the sheath.
 4. The system of claim 1, whereinthe strippable sheath includes at least one strand, segments of thestrand each having a first portion formed in a first loop wrapped on themedical apparatus and an adjacent second portion formed in a second loopwrapped on the medical apparatus and passing through the first loop. 5.The system of claim 4, wherein the second loop passes through a firstloop of a neighboring segment of the strand.
 6. The system of claim 4,wherein the strand includes a releasable knot retaining a portion of thestrand at an end of the sheath.
 7. The system of claim 1, wherein themedical apparatus is a prosthesis implantable in the body.
 8. The systemof claim 7, wherein the prosthesis is a mesh tube including metalmaterial.
 9. The system of claim 8, wherein the prosthesis includesknitted thread material.
 10. The system of claim 4, further comprising acatheter having a distal end portion for insertion in the body and aproximal end portion, the medical apparatus being on the distal endportion of the catheter.
 11. The system of claim 4, wherein the sheathreleasably retains the medical apparatus on the distal end portion ofthe catheter, the medical apparatus being releasable from the catheterwhen the sheath is stripped.
 12. The system of claim 10, wherein themedical apparatus is a prosthesis implantable in the body.
 13. Thesystem of claim 12, wherein the prosthesis is a mesh tube includingmetal material.
 14. The system of claim 12, wherein the prosthesisincludes knitted thread material.
 15. The system of claim 11, whereinthe medical apparatus is a prothesis implantable in the body.
 16. Thesystem of claim 10, wherein the catheter has at least one lumenextending from the distal end portion of the catheter to the proximalend portion of the catheter, the drawstring extending through the lumen.17. The system of claim 10, wherein the sheath comprises at least onestrand and the system further comprises a cuff on the catheter, the cuffreleasably restraining a portion of the strand to an outer surface ofthe catheter.
 18. The system of claim 10, wherein the catheter includesat least one lumen allowing for bodily insertion of the catheter over aguide wire.
 19. The system of claim 18, further comprising a flexibleguide wire inserted in the lumen.
 20. The system of claim 1, furthercomprising an additional sheath on the medical apparatus between themedical apparatus and the strippable sheath.
 21. The system of claim 1,wherein the medical apparatus includes a drug capable of being releasedwhen the medical apparatus is in the body.
 22. The system of claim 1,wherein the medical apparatus includes material dissolvable in the bodywhen the medical apparatus is deployed.
 23. The system of claim 7,wherein the prosthesis comprises crocheted thread material.
 24. A systemfor use in medical treatment of a body, comprising:a medical apparatushaving a distal end and a proximal end, the medical apparatus beingexpandable between a reduced profile and an expanded profile; and athread-like strand maintaining the medical apparatus in the reducedprofile and having releasable knots, the releasable knots extending thelength of the apparatus, the releasable knots being released by pullingan end portion of the strand to allow the medical apparatus to expandinto its expanded profile.
 25. The system of claim 24 wherein the strandfurther comprises a drawstring attached to the end of the strand that ispulled to release the releasable knots.
 26. The system of claim 24wherein the system further comprises a catheter onto which the medicalapparatus is mounted, the catheter having a proximal end and a distalend, the medical apparatus being disposed at the distal end of thecatheter and the drawstring extending toward the proximal end of thecatheter.
 27. The system of claim 26 wherein the catheter includes acuff mounted on the catheter adjacent to the proximal end of the medicalapparatus.
 28. The system of claim 24 wherein the strand includessegments having a first portion formed in a loop wrapped on the medicalapparatus and an adjacent second portion formed in a second loop wrappedon the medical apparatus and passing through the first loop.
 29. Thesystem of claim 28 wherein the second loop passes through the first loopof a neighboring segment of the strand.
 30. The system of claim 24wherein the releasable knots are configured to allow the medicalapparatus to expand from one axial end to the other.
 31. The system ofclaim 30 wherein the releasable knots are configured to release themedical apparatus from a distal end of the medical apparatus to theproximal end of the medical apparatus.
 32. The system of claim 24wherein the medical apparatus is self-expandable from the reducedprofile to the expanded profile when the releasable knots are released.33. The system of claim 24 wherein the medical apparatus is a stent. 34.The system of claim 33 wherein the stent is a mesh tube including metalmaterial.
 35. The system of claim 33, wherein the stent includes bentthread-like material.
 36. The system of claim 24, wherein the medicalapparatus is a prosthesis implantable in the body.
 37. The system ofclaim 36, wherein the prosthesis is a mesh tube including metalmaterial.
 38. The system of claim 36, wherein the prosthesis includesknitted thread material.
 39. The system of claim 32, wherein the medicalapparatus is a prosthesis implantable in the body.
 40. The system ofclaim 26, wherein the catheter has at least one lumen extending from thedistal end portion of the catheter to the proximal end portion of thecatheter, the drawstring extending through the lumen.
 41. The system ofclaim 40, further comprising a cuff on the catheter, the cuff releasablyretaining a portion of the strand to an outer surface of the catheter.42. The system of claim 26, wherein the catheter includes at least onelumen allowing for bodily insertion of the catheter over a guide wire.43. The system of claim 42, further comprising a flexible guide wireinserted in the lumen.
 44. The system of claim 24, further comprising asheath on the medical apparatus between the medical apparatus and thethread-like strand.
 45. The system of claim 25, wherein the medicalapparatus includes a drug capable of being released when the medicalapparatus is in the body.
 46. The system of claim 24, wherein thethreadlike strand includes material visible during x-ray imaging. 47.The system of claim 25, wherein at least the drawstring includesmaterial visible during x-ray imaging.
 48. The system of claim 24,wherein the medical apparatus includes material dissolvable in the bodywhen the medical apparatus is deployed.
 49. The system of claim 36,wherein the prosthesis comprises crocheted thread material.
 50. Thesystem of claim 1, wherein the sheath is a mesh.